Metric practices shall conform to IEEE/ASTM SI 10. Preference shall
be given to expressing measurements in metric units, if practicable. The
SD-10 provides guidance on when to develop a metric specification or to
convert inch-pound specifications to metric.

4.8.1 Metric unitsMetric units shall be in accordance
with IEEE/ASTM SI 10. Metric sizes should generally be expressed in
whole numbers. There shall be no soft conversion of units merely for the
sake of conversion.

4.8.2 Dual dimensionsWhen preference is given to
inch-pound units, acceptable metric units may be shown in parentheses.
When preference is given to metric units, inch-pound units may be omitted or
included in parentheses. The mixed use of both metric and inch-pound as
primary measurements should be avoided.